Effect Of Subchronic Cadmium Poisoning On Oxidative Damage And Apoptosis In Rat Kidney And The Protective Effect Of Vitamin E

Cadmium（Cd）,a widely distributed heavy metal pollutant in the environmental,is extremely toxic to kidney.Cd exposure can induce oxidative stress and apoptosis in the kidney.Vitamin E（VE）is a kind of fat-soluble vitamin with the functions of scavenging free radicals and anti-oxidation.At present,there have been some reports on the effects of Cd poisoning on oxidative damage and apoptosis in rat kidneys and the protective effect of VE,however,the related mechanism is not fully understood.The purpose of this study was to investigate the effects of subchronic Cd poisoning on oxidative stress,Nrf2signaling pathway,apoptosis and apoptotic related regulatory molecules in rat kidney,and the protective mechanism of VE.In this study,32 nine-week-old male Sprague-Dawley rats were randomly divided into four groups,namely control,VE（100 mg/kg VE）,Cd（5 mg/kg CdCl2）and VE+Cd（100 mg/kg VE+5 mg/kg CdCl2）,and received intragastric administration of Cd and/or VE for 28 days.Histopathological techniques,atomic absorption spectrometry,biochemical method,TUNEL assay,relative real-time fluorescent quantitative PCR（RT-q PCR）and Western blotting analysis were used to study the effects of Cd on the blood urea nitrogen（BUN）and serum creatinine（Scr）levels,along with renal morphology,Cd content,oxidative stress levels,Nrf2 signaling pathway and apoptosis,as well as the protective effects of VE on the above mentioned parameters.The results are as follows:1.After 14,21 and 28 days of the experiment,the body weight of the Cd group was significantly decreased in comparison with the control and VE+Cd groups（P<0.05 or P<0.01）;at the 28 days of the experiment,compared with the control and VE+Cd groups,the kidney weight in the Cd group was significantly decreased（P<0.01）;there was no significant difference（P>0.05）in the kidney index among the four groups.2.After 28 days of the experiment,compared with the control group,the Cd concentrations of the kidney in the Cd and VE+Cd groups were significantly increased（P<0.01）;no significant differences（P>0.05）in the Cd concentration of the kidney was found between the Cd and VE+Cd groups.Compared with the control and Cd groups,the VE concentration of the kidney in the VE and VE+Cd groups was significantly increased（P<0.01）;there was no significant difference（P>0.05）in the VE concentration of the kidney between the control and Cd groups.3.After 28 days of the experiment,in comparison with the control and VE group,the levels of BUN and Scr in the Cd group were significantly increased（P<0.01）;the values in the VE+Cd group were significantly decreased（P<0.05 or P<0.01）compared with the Cd group;there was no significant difference in these parameters between the VE and control groups（p>0.05）.4.After 28 days of the experiment,histopathological alterations were observed in the Cd group,including swollen glomerulus along with narrowed capsular space,cytoplasmic granule degeneration in the epithelial cells of some renal tubules in the cortex,pyknotic nuclei with condensed chromatin in the epithelial cells of proximal convoluted tubules and collecting ducts,and hemolysis and hemorrhage in partial area;compared with the Cd group,the degree of glomerular swelling and renal capsule stenosis in the VE+Cd group was significantly improved;the granule degeneration of renal tubular epithelial cells was significantly reduced;the number of pyknotic nuclei in the epithelial cells of proximal convoluted tubules and collecting ducts was slightly reduced,and the degree of cortical hemolysis and hemorrhage was slightly decreased.5.After 28 days of the experiment,compared with the control and VE group,Cd-exposure significantly increased（P<0.01）the renal MDA content,decreased（P<0.05 or P<0.01）the GSH and T-AOC contents,as well as the antioxidant enzymes（SOD,CAT,GSH-PX）activities accompanied by decreased（P<0.01）the m RNA and protein expressions of Nrf2 signaling pathway related factors（Nrf2,HO-1,NQO-1,GCLC,GCLM and GST）;compared with the Cd group,the change range of the above indicators in VE+Cd group were significantly reduced（P<0.05 or P<0.01）;these values showed no significant difference between the VE and control groups（p>0.05）.6.After 28 days of the experiment,in comparison with the control and VE groups,the number of TUNEL-positive cells and the m RNA and protein expression levels of apoptotic regulatory molecules（Bax,Caspase-3,GRP94,GRP78 and Caspase-8）were significantly increased（P<0.01）,while Bcl-2 expression levels was significantly reduced（P<0.01）;compared with the Cd group,the VE+Cd group showed a significant decrease（P<0.05 or P<0.01）in these indicators mentioned above（Bax,Caspase-3,GRP94,GRP78 and Caspase-8）except for Bcl-2 expression which was increased;there was no significant difference in these parameters between the VE and control groups（P>0.05）.In conclusion,administration of CdCl₂（5mg/kg）to rats by gavage for 28 days significantly reduced the body weight and kidney weight,elevated the levels of BUN and Scr as well as the accumulations of Cd in the kidney,caused renal histological alteration,increased renal MDA content and decreased the GSH and T-AOC contents,as well as the antioxidant enzymes（SOD,CAT and GSH-PX）activities accompanied by decreased expressions of Nrf2 signaling pathway related factors,while increased expressions of apoptotic regulatory molecules,ultimately causing renal oxidative damage and excessive apoptosis.However,the supplementation of VE（100 mg/kg）could alleviate the reduction of the body weight and kidney weight in rats to a certain extent,improve kidney tissue structure and function damage,increase antioxidant enzyme activity and non-enzyme antioxidant content,and upregulate the expressions of Nrf2 signaling pathway and down-regulate the expressions of apoptotic regulatory molecules,thereby protecting Cd-induced renal oxidative damage and excessive cell apoptosis.